The present invention relates to an electromagnetic and thermal shield for an energy meter having a transparent glass or polycarbonate housing, particularly where the energy meter is of the electronic type.
Energy meters are installed and utilized in millions of different locations, many of which are exposed to very high temperatures, including direct sunlight, and also exposed to electromagnetic interference which could adversely affect the operation of the electronic energy meter. Direct sunlight shining through the transparent housing results in a greenhouse effect in which the interior of the energy meter tends to reach extremely high temperatures, much higher than the ambient temperature outside the meter.
While it is conventional to have a transparent housing for an energy meter to permit the reading of the visual displays of the energy meter by the customer or meter reader, it is not desirable to have the component parts, including the electronics of the meter, visible from the outside, not only from a heat and electromagnetic radiation point of view, but also from an aesthetic point of view.
Various approaches to providing electromagnetic and thermal shields for energy meters have been proposed or utilized, including that disclosed, for example, by U.S. Pat. No. 4,795,975 in which a thermal and electromagnetic shield is fabricated of organic layers bonded to a foil layer through use of intermediate adhesives. The resultant pliable thermal and electromagnetic shield presents possible problems of grounding, retention of shape, and concern that the pliable shield might accidentally make electrical contact with voltages within the energy meter. It is desirable that the electromagnetic and thermal shield be rigid and provide a positive ground on contact.
In addition, the energy meter may be constructed in a layered configuration, that is, with a base assembly and a register or meter assembly spaced from the base assembly with an intermediate electronic layer. In such meters means must be provided to support these multiple layers relative to one another, and also to prevent dangerous shock from the voltages present within, and between, these layers when the cover is removed, for example, to actuate certain test or other functions built into the meter.